If Snowy barks at certain visitors, ask them to kneel down to his level and try to pet him. Remember to tell them to extend their hand with the palm downward or else Snowy may think they are trying to hurt him. A treat also helps. But if Snowy continues to bark at them, just ask them to leave him a lone and put Snowy in another room. This will teach him that he can not "hang out" if he is going to act like that. Make sure your guests do not force themselves on Snowy and try to pet or play with him without his consent. Snowy may snap and bite them. I have seen it happen many times. This upsets everyone, you, Snowy, and your visitors.
About the car. 10 lbs. is small enough for you to carry him and put him in the car. Take him to the park or somewhere you think he will like (lake, stream, a trail where you can both walk together) or even for a ride. Be sure to give him a treat if he is quiet int the car and well behaved, and treat him when you get home. After a couple of times, he will no longer associate the car with the vet!
Good luck!